1. Field of the Invention.
The present invention relates to pallet-making machines, and in particular to nail-driving chucks for use in a pallet-making machine.
2. Description of the Prior Art.
Wooden pallets, as they are known today, first came into widespread use during World War II as a result of the need of the United States Navy to move large amounts of goods in short periods of time with forklift trucks. The usage of wooden pallets has increased every year since that time.
In 1987, it is projected that about 380 million new wooden pallets will be built in the United States. Pallets consume about twenty percent of the lumber that is used in the United States annually. The manufacture of pallets is second only to the construction industry and is ahead of all other industries in the use of lumber. Wooden pallets consume about fifty percent of the hardwood lumber used annually in the United States.
To satisfy the high demand for wooden pallets, machines have been developed which manufacture pallets on a semi-automatic or automatic basis. An example of automated pallet-making equipment is shown in the Colson U.S. Pat. No. 3,945,549.
The Colson patent shows a type of pallet-making machine which uses a special vibrating bowl to feed bulk nails to picker mechanisms, which individually feed the nails to chucks. Each time a nailing operation is to take place, a ram drives the nail being held by the chuck into the boards located below the chuck. The special vibrating bowl, which feeds bulk nails to several different chucks, has been found to be very difficult to implement in practice.
An alternative approach for feeding bulk nails is to use a separate vibrating bowl for each chuck. While this simplifies the construction of the bowl, it greatly increases the cost of the machine because three or four vibrating bowls, with their associated drive mechanisms, must be provided.
The other common approach for pallet-making machines has been to use collated nails (i.e. nails which are carried by or attached to a flexible strip). The strip is fed to a nail gun which fires the nail into the wood at a very high velocity using air for power.
The use of a nail gun and collated nails has several significant disadvantages. First, the cost of collated nails is several times that of bulk nails. Second, nail guns, which rely on firing a nail into the wood at very high velocity, are prone to board splitting. In addition, because the nail gun is typically hand-held by the operator, nail placement is not repeatable.